Gas discharge devices (such as lasers) typically operate by exciting a gas, such as neon, helium, or carbon dioxide (CO.sub.2), to a highly ionized plasma state and producing coherent light when the excited gas emits light of a characteristic energy (i.e., discharging). The gas, which is generally retained under pressure in a closed vessel, is excited to the higher energy, plasma, state in a discharge region located between two electrodes. The plasma is generally formed by imposing a high voltage between electrodes disposed on opposite sides of the discharge region.
Once the gas discharge device has begun to produce its light, it enters a self-sustaining mode. In this mode, the gas contained in the discharge region carries a current in excess of a characteristic threshold level (the sustaining current) and, as a result, sustains its own discharge for an extended period of time.
A gas discharge device operates in a pulsed mode, since the energy produced in the form of light must be refreshed from time to time by re-imposing the voltage across the discharge region. The pulses are typically 10 to 20 microseconds in duration.
If the gas discharge device is a laser, two optical assemblies, such as mirrors, are located at opposite sides of the pressure vessel. At least one of the optical assemblies is partially transmissive. The optical assemblies cause the discharge light beam to be reflected therebetween and define an optical axis for the laser light that passes through the partially transmissive optical assembly.
It has been found that a self-sustaining gas discharge device can produce longer pulses than are otherwise possible if the gas in the discharge region is maintained in an ionized state while it is discharging. An electron beam is a particularly convenient way of ionizing the gas in the discharge region. However, external electron beam sources for producing long duration electron beams are fragile and cumbersome.
It is therefore desirable to have a long pulse self-sustaining gas discharge device without the requirement of using a long duration electron beam source.